BACnet Binary Output Object

The BACnet Binary Output object (Clause 12.7) is a commandable two-state output: its priority array, minimum on/off times

Categories:

BACnet

Tags:

Bacnet Object Type Binary Output

Updated

Jul 15, 2026

What the Binary Output Object Is

The Binary Output object, defined in Clause 12.7 of ANSI/ASHRAE 135-2024, is how a BACnet device represents a two-state output it drives: a relay, a stage, or an on/off command. Where a Binary Input reports a contact you cannot change, a Binary Output is commandable, and clients write active or inactive to switch it.

Like the Analog Output, a Binary Output is commanded through a 16-slot priority array rather than a single writable value, so multiple controllers and operators can command the same output without conflict. It also adds Polarity (the input-style physical mapping) and two properties unique to switched loads: Minimum_On_Time and Minimum_Off_Time, which protect equipment from short-cycling. Binary Output objects that support intrinsic reporting apply the CHANGE_OF_STATE event algorithm.

Where You’ll See It

Relay and stage control. Starting a fan, energizing a stage of heating, or switching a pump.
Enable and command points. An operator or sequence turning equipment on and off from the head end (the central BMS server).
Short-cycle protection. With Minimum_On_Time and Minimum_Off_Time, a Binary Output enforces a runtime floor so a compressor or motor is not switched too rapidly.

How Commanding Works

A WriteProperty to Present_Value does not set the output directly. It places active or inactive in one of 16 slots of the Priority_Array, chosen by the write’s priority (1 = highest, 16 = lowest). The object drives the highest-priority non-Null slot; writing Null at a priority relinquishes that command, and when every slot is Null the object falls back to Relinquish_Default. Current_Command_Priority reports the active slot. This is the same model the Analog Output uses, applied to a two-state value.

Required Properties

Clause 12.7 requires every Binary Output object to provide these properties. Datatypes are the spec’s names: BACnetBinaryPV is the two-state present value (active or inactive), BACnetPriorityArray is the 16-slot command array, and the other BACnet-prefixed types are structured values defined by the standard.

Property	Datatype	What it holds
`Object_Identifier`	BACnetObjectIdentifier	The object’s type and instance number, unique within the device
`Object_Name`	CharacterString	The human-readable point name, unique within the device
`Object_Type`	BACnetObjectType	Always `binary-output` for this object
`Present_Value`	BACnetBinaryPV	The commanded state. Writable, but through the priority array, not as a direct store
`Status_Flags`	BACnetStatusFlags	Four health flags: in-alarm, fault, overridden, out-of-service
`Event_State`	BACnetEventState	The object’s current event state (normal, off-normal, or fault)
`Out_Of_Service`	BOOLEAN	When true, `Present_Value` is decoupled from the physical output for testing
`Polarity`	BACnetPolarity	Maps the logical state to the physical signal (normal or reverse)
`Priority_Array`	BACnetPriorityArray	The 16 command slots; the highest-priority non-`Null` slot wins
`Relinquish_Default`	BACnetBinaryPV	The state the output takes when every priority slot is `Null`
`Current_Command_Priority`	BACnetOptionalUnsigned	Which priority slot (1-16) is currently in control, or none
`Property_List`	BACnetARRAY[N] of BACnetPropertyIdentifier	The list of properties this instance actually implements

Optional Properties

The properties integrators meet most are Minimum_On_Time and Minimum_Off_Time (short-cycle protection), the state labels Inactive_Text and Active_Text, and Feedback_Value (the sensed actual state, for proving the command took effect). The intrinsic-reporting group generally appears or is absent as a set.

Property	Datatype	Group
`Description`	CharacterString	General
`Device_Type`	CharacterString	General
`Inactive_Text`	CharacterString	State labels
`Active_Text`	CharacterString	State labels
`Minimum_Off_Time`	Unsigned32	Switching protection
`Minimum_On_Time`	Unsigned32	Switching protection
`Change_Of_State_Time`	BACnetDateTime	Runtime tracking
`Change_Of_State_Count`	Unsigned	Runtime tracking
`Time_Of_State_Count_Reset`	BACnetDateTime	Runtime tracking
`Elapsed_Active_Time`	Unsigned32	Runtime tracking
`Time_Of_Active_Time_Reset`	BACnetDateTime	Runtime tracking
`Feedback_Value`	BACnetBinaryPV	Commanding
`Value_Source`	BACnetValueSource	Commanding
`Value_Source_Array`	BACnetARRAY[16] of BACnetValueSource	Commanding
`Last_Command_Time`	BACnetTimeStamp	Commanding
`Command_Time_Array`	BACnetARRAY[16] of BACnetTimeStamp	Commanding
`Time_Delay`	Unsigned	Intrinsic reporting
`Notification_Class`	Unsigned	Intrinsic reporting
`Event_Enable`	BACnetEventTransitionBits	Intrinsic reporting
`Acked_Transitions`	BACnetEventTransitionBits	Intrinsic reporting
`Notify_Type`	BACnetNotifyType	Intrinsic reporting
`Event_Time_Stamps`	BACnetARRAY[3] of BACnetTimeStamp	Intrinsic reporting
`Event_Message_Texts`	BACnetARRAY[3] of CharacterString	Intrinsic reporting
`Event_Message_Texts_Config`	BACnetARRAY[3] of CharacterString	Intrinsic reporting
`Event_Detection_Enable`	BOOLEAN	Intrinsic reporting
`Event_Algorithm_Inhibit_Ref`	BACnetObjectPropertyReference	Intrinsic reporting
`Event_Algorithm_Inhibit`	BOOLEAN	Intrinsic reporting
`Time_Delay_Normal`	Unsigned	Intrinsic reporting
`Reliability`	BACnetReliability	Fault detection
`Reliability_Evaluation_Inhibit`	BOOLEAN	Fault detection
`Audit_Level`	BACnetAuditLevel	Auditing
`Auditable_Operations`	BACnetAuditOperationFlags	Auditing
`Interface_Value`	BACnetOptionalBinaryPV	Integration
`Tags`	BACnetARRAY[N] of BACnetNameValue	Tagging and profile
`Profile_Location`	CharacterString	Tagging and profile
`Profile_Name`	CharacterString	Tagging and profile

Binary Input: the read-only two-state counterpart for contacts and statuses.
Binary Value: a two-state software point (a mode or enable flag).
Analog Output: the modulating equivalent, with the same priority-array model.

What Chipkin Provides

The Binary Output object, including the priority array, minimum on/off timing, and CHANGE_OF_STATE intrinsic reporting, is a first-class object type in the CAS BACnet Stack. Talk to us about modeling your device’s points.